The present invention is concerned with an aircraft rib assembly. More particularly, the present invention is concerned with an aircraft rib assembly suitable for attachment of an aircraft control surface at any of a number of positions along the spar of an aircraft wing, vertical stabiliser or horizontal stabiliser.
It is desirable to mount movable control surfaces such as inter alia flaps, slats, ailerons and rudders to fixed aerodynamic structures such as wings and stabilisers (e.g. vertical or horizontal stabilisers). This is usually achieved using a fixed rib which extends from a structural component of the fixed structure (such as a fore or aft rib) to the mounting point of the relevant control surface.
In one example, spoilers are aerodynamic devices which are attached to the trailing edge of aircraft wings in order to disrupt the boundary layer flowing across the wing during flight. They are used to reduce the aerodynamic effect of the wing in order to decrease lift and increase drag to slow the aircraft.
Known spoilers are mounted using a spoiler rib which projects rearwardly from the rear spar of the wing. The rib comprises a spoiler attachment point lug at the rear, a first limb and a second limb both projecting from the attachment point at an angle to each other, forming a “V”. The rib is attached to the wing at two points. The first limb is attached at an upper point where the rear spar meets the upper wing skin. The second limb is attached at a lower point where the spar meets the lower wing skin. At both points the rib is mechanically fastened to both the spar and the skin.
Fastening at the top and bottom of the spar provides the largest moment arm to react the forces experienced by the spoiler in flight.
Although optimised for load reaction, a problem with this design is that because the rib needs to be attached at the extreme top and bottom of the rear spar, each rib must be individually manufactured for its position along the wingspan because the depth of the spar reduces from fuselage to wing tip.
A further disadvantage of the prior art is that the geometry of the wing skin is somewhat variable (particularly for in-service aircraft) and, as such, some shimming or fettling of the rib is required in order to securely fix it in place.
Because of wing bending in flight, the upper and lower wing skins are subject to high strains. This necessitates bolts of a high diameter between the wing skin overhang and the ribs, and also thick skin material at the rib attachment positions. It is generally not practical to make the wing skin locally thicker at these points and, as such, the thickness is carried throughout the wingspan which adds significant weight to the aircraft. The additional weight in order to support this structural requirement may be as much as 10 kg per meter of wingspan.
Finally, struts supporting the lower shroud panel have to be fastened onto the ribs by means of bolt-on support brackets which constitute additional parts and require more expensive assembly.
Similar problems arise with other control surfaces mounted to fixed aerodynamic structures, for example ailerons mounted to the trailing edge of wings and horizontal stabilisers, and rudders mounted to the trailing edge of vertical stabilisers.